When I first started making chairs, I notice that my scraping and sanding process would sometimes allow the grain of the pine to show through nicely. The problem was that I couldn't control it. So I set about finding the right steps to take to show the grain.
Here is a photo of a newly scraped seat. You can see that I've wet part of it and the grain has raised. When scraping the seat, the denser part of the growth rings cuts cleanly while the softer wood compresses just a bit. Later when the paint hits it, the softer wood absorbs the moisture and pops up, revealing the grain. That's how I understand it, now to control it.
To get consistent results requires a very sharp and finely honed scraper. No scratchy file marks or ragged burrs. I scrape the chair as though sandpaper will never touch it (it barely does). Using a raking light and moving the chair around will help you to see any problem areas and running the palm of your hand to feel the surface helps too.
Once the surface looks perfectly smooth and shaped, I sand very lightly with 220 grit. Next, I like to use a walnut hull stain to raise the seat grain. It shows any unsightly problems. If there is a trouble area, I let the seat dry and rescrape and repeat the sanding and staining. Once the grain is raised and I like the results, I move on to painting. I let the first coat dry hard and then sand very lightly with 220 grit again. This should cut through the high spots and give a clear vision of the grain that will be visible. Oversanding at this point will result is smooth patternless areas in the final seat. Then I finish painting the chair, no more sanding.
I suppose the best way to gain experience with this technique is to do sample and eliminate the sanding altogether. This way you will see the results of your scraping technique and the phenomenon of the compressed/raised grain. The sanding is really just to knock down fuzz and can be introduced later.